Let's say Amazon stock doubles in the first two years you work there. So maybe your TC was $250K your first two years, but if you stay that third year, you'll vest in $500K in stock, and if it keeps going up, that fourth year might be $800K in stock (which up until 18 months ago was pretty common).

So you'll get people who can't walk away because they can't get TC of $500K somewhere else.